Iron nitride magnetic powder and method of producing the powder

a technology of iron nitride and magnetic powder, which is applied in the field of iron nitride magnetic powder and method of producing powder, can solve the problems of inability to realize sufficient resolution, inability to record, and phenomena cannot be eliminated, and achieve excellent magnetic properties, good oxidation resistance, and high hc and low bsfd.

Inactive Publication Date: 2005-06-09
DOWA ELECTRONICS MATERIALS CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0017] An object of the present invention is therefore to provide an Fe16N2 system iron nitride powder that achieves excellent magnetic properties enabling use in a high-recording density magnetic medium, particularly high Hc and low BSFD, together with good oxidation resistance.

Problems solved by technology

If it is not, a distinct magnetic transition cannot be produced, making practical recording impossible.
Even if such a magnetic powder should be obtained, various problems will nevertheless arise if the thickness of the magnetic layer obtained by applying the powder in the form of a coating material is too thick.
This is because self-demagnetization loss, thickness-loss attributable to magnetic layer thickness and other such problems that are not major issues when using conventional long recording wavelengths come to have a pronounced effect and give rise to phenomena that, for instance, make it impossible to realize sufficient resolution.
Such phenomena cannot be eliminated only by enhancing the magnetic properties of the magnetic powder or improving surface properties by application of medium production technologies.
However, when particle refinement reaches the point that the decrease in particle volume exceeds a certain degree, a marked degradation of magnetic properties occurs owing to thermal fluctuation, and when particle size decreases still further, superparamagnetism is exhibited and magnetism ceases to be exhibited.
Another problem is that the increase in specific surface area with increase in particle size refinement degrades oxidization resistance.
No magnetic material having these properties has been put to practical use heretofore.
Therefore, when such a magnetic powder is used in a coating material for preparing a tape to be used as a high-density recording medium, noise readily occurs.
Moreover, when low Hc components are present, such particles are apt to experience erasure of recorded content because they cannot maintain magnetism owing to thermal fluctuation, so that a reliability problem arises.
Thus there has not been known a method that can effectively improve the oxidation resistance of an iron nitride magnetic powder comprising Fe16N2 while maintaining its high Hc, high as and low SFD unchanged.

Method used

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Examples

Experimental program
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Effect test

example 1

[0043] As starting material was used a powder composed of 27 nm average diameter magnetite particles having a surface layer of Si and Y oxides (Si and Y content expressed as atomic percent based on Fe of 4.7 at. % and 1.0 at. %, respectively). The powder was placed in a furnace, heated, and reduced in a stream of hydrogen gas at 500° C. for one hour. It was then cooled to 100° C., at which temperature the gas of the gas stream was changed from hydrogen to ammonia, and thereafter heated to 165° C. At this temperature, the outlet pressure of the discharge gas was regulated to put the furnace under a controlled pressurized condition of 0.1 MPa. Nitriding was conducted for 11 hours under this pressurized condition.

[0044] After the nitriding treatment, the outlet pressure of the discharge gas was returned to atmospheric pressure to discontinue the pressurization, whereafter the temperature was lowered to 80° C. and the gas of the gas stream was changed to nitrogen gas to which was added...

example 2

[0047] Example 1 was repeated except that the outlet pressure of the discharge gas was regulated to put the furnace under a controlled pressurized condition of 0.3 MPa.

[0048] The powder obtained had an average particle diameter of 25 nm and a BET specific surface area of 44 m2 / g. The results of magnetic property evaluation were: Hc=239 KA / m, σs=97 AM2 / Kg, and BSFD=1.31. The powder oxidation resistance Δσs was 23.7% and the ratio below Hc 120 KAm in the BSFD was 9.3%. The evaluated tape properties were: Hcx=265 KA / m, SFDx=0.56, SQx=0.75, and tape oxidation resistance ΔBm of 11.8%.

example 3

[0049] Example 1 was repeated except that the starting material used was 20 nm average diameter goethite particles containing Al and Y as sinter preventing agents at atomic percents based on Fe of 9.4 at. % and 1.9 at. %, respectively.

[0050] The powder obtained had an average particle diameter of 15 nm and a BET specific surface area of 69 m2 / g. The results of magnetic property evaluation were: Hc=214 KA / m, σs=67 Am2 / Kg, and BSFD=1.77. The powder oxidation resistance Δσs was 35.3% and the ratio below Hc 120 KAm in the BSFD was 13.2%. The evaluated tape properties were: Hcx=233 KA / m, SFDx=0.71, SQx=0.70, and tape oxidation resistance ΔBm of 16.8%.

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Abstract

An iron nitride magnetic powder comprised primarily of Fe16N2 phase is characterized in that its coercive force Hc is 200 KA/m or greater and bulk switching field distribution BSDF is 2 or less. The magnetic powder can be produced by allowing a nitriding reaction of Fe particles with a nitrogen-containing gas for producing nitrided particles of primarily Fe16N2 phase to proceed under an increased pressure of 0.1 MPa or greater. The enhanced properties of the iron nitride magnetic powder make it suitable as a magnetic material for high-density magnetic recording media.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] This invention relates to an iron nitride magnetic powder suitable for constituting the magnetic layer of a high recording density medium and a method of producing the powder. [0003] 2. Background Art [0004] In order to achieve the increasingly higher recording density required by today's magnetic recording media, efforts are being made to enable use of shorter recording wavelengths. For this, it is necessary to make the magnetic particle size much smaller than the length of the region for recording the short-wavelength signal. If it is not, a distinct magnetic transition cannot be produced, making practical recording impossible. The particle size of the magnetic powder is therefore required to be sufficiently small. [0005] To realize higher recording density, the resolution of the recording signal must be increased. Reduction of magnetic recording medium noise is therefore important. Noise is largely attributable t...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): B22F9/00H01F1/01C01B21/06C22C29/16G11B5/706H01F1/047H01F1/053H01F1/06
CPCB82Y30/00C01B21/0622C01P2004/64C01P2006/37C01P2006/42Y10T428/2982H01F1/065Y10T428/2993Y10T428/2995Y10T428/12181Y10T428/2991G11B5/70626C22C29/16
Inventor MASADA, KENJIAMINO, TAKAFUMINAGATOMI, AKIRA
Owner DOWA ELECTRONICS MATERIALS CO LTD
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